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Subject: Re: [LML] Re: the Legacy RG Static ports
From: Paul Besing <paulbesing@me.com>
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Then it must have been an RV specific requirement=85location of the =
port, who knows=85but my errors were significant with a flush static =
port, and were very accurate with a protruding port.  I am not an =
engineer but the data on that airplane was evident. =20


--
Paul Besing
"Flying releases the mind from the tyranny of petty things"


On Jan 22, 2013, at 8:12 AM, Charles Brown <browncc1@verizon.net> wrote:

> Guys, I am astonished to hear anyone advocating a protruding static =
port and especially for the purpose of sticking out of the boundary =
layer.   I worked on the critical altimetry for reduced vertical =
separation minimums at Boeing in the mid-90s and on air data systems at =
General Dynamics (now Lockheed).  On every airplane and missile design =
I've ever worked on, the only reason to make a static port anything =
other than perfectly flush was to insert a correction if the static port =
was located in a place where the local pressure was different from =
ambient pressure.  Projecting anything with an edge or corner out of the =
boundary layer was guaranteed to produce local separation and vortices =
with unpredictable and probably inconsistent effects on the measured =
pressure.   On Boeings, we even went to great lengths to measure and =
minimize skin waviness for 10 feet ahead of the static ports.
>=20
> The static pressure gradient across the boundary layer is generally =
accepted to be negligible. =20
>=20
> A protruding static port will probably measure pressure that's a =
little lower than the local static pressure, which is acceptable only if =
the port is located in an area with higher than ambient pressure.   =
Perhaps Paul's RV ports were located in such an area.
>=20
> Lancair tech support (whoever it was who answered the phone in 2008) =
told me to make them flush.  I presume that the port  position that they =
identified on the Legacy is where the local Cp is zero, i.e., ambient =
pressure.  At any rate, my flush ports seem to work fine.  If you have a =
Garmin, a good test is to fly a closed course and see if the deduced =
wind value is consistent on all headings.  If it is, then a number of =
things (magnetometer alignment, pitot pressure, static pressure, and =
OAT) are working correctly.=20
>=20
> Charley Brown
> Legacy #299  200 hr
>=20
>=20
> On Jan 21, 2013, at 7:06 PM, Paul Besing wrote:
>=20
> Yes, it has to protrude out about 3/16" on average.  I had this exact =
problem with my RV.  I decided I wanted a nice flush look and my =
airspeed were very inaccurate until it was discovered that they needed =
to come out of the boundary layer.=20
>=20
>=20
> --
> Paul Besing
> "Flying releases the mind from the tyranny of petty things"
>=20
>=20
>=20
> On Jan 22, 2013, at 1:25 AM, Dan Ballin <dballin@gmail.com> wrote:
>=20
>> Needs to protrude a little for paint/body work and then there is an
>> argument to have them stick out slight more to get out of the =
boundary
>> layer.  Others can comment on that, but I would recommend using the
>> Evo static ports.  KCI part number KA0075.  Way nicer and have a
>> standard NPT thread so easier to install and you can install it after
>> paint.
>>=20
>> Dan
>> N386DM LEG2
>>=20
>>=20
>>=20
>> On Mon, Jan 21, 2013 at 11:47 AM, Jeffrey W. Skiba <jskiba@icosa.net> =
wrote:
>>> on page Chapter 24 REV. 0/02-15-02 of the Legacy RG construction =
manual,
>>> gives directions for the static ports, however it does not state if =
they
>>> should be flush with the skin or slightly protrude ? if they need to =
stick
>>> out Is there a max and a min suggested ?
>>>=20
>>>=20
>>>=20
>>> Thanks
>>>=20
>>> Jeff.
>>>=20
>>>=20
>> <Screen Shot 2013-01-21 at 11.57.56 AM.png>--
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>=20
>=20
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